1. Field of the Invention
The present invention relates to a toner-amount-regulating elastic blade which regulates the amount of a toner for developing an electrostatic latent image formed on an image bearing member in order to provide a visual image, and a developing device and an apparatus unit using such a blade.
2. Description of the Related Art
An elastic blade comprising a supporting plate and a rubber elastic member supported thereon is known as an elastic blade for regulating the amount of a toner coated on the surface of a toner bearing member.
FIG. 2 illustrates a developing device using such an elastic blade. This developing device includes a toner bearing member mounted in a toner chamber 2, a toner-amount regulating elastic blade 4, an elastic roller 5, and a toner 6. An electrophotographic photosensitive member 1 faces the toner bearing member 3 with a very small gap therebetween. The toner bearing member 3 carries the toner 6 to a developing portion. By contacting the elastic blade 4, which serves as means for regulating the thickness of the layer of the toner 6 on the toner bearing member 3 to a thin value, to the toner bearing member 3, and regulating the toner 6 passing through a contact portion between the elastic blade 4 and the toner bearing member 3, a thin layer of the toner 6 is formed on the toner bearing member 3. The toner 6 is provided with triboelectric charges for developing a latent image by friction at the contact portion. The elastic blade 4 includes a supporting plate 4a and an elastic member 4b supported thereon.
A rubber plate, a metallic thin plate, a resin thin plate, a lamination of these plates, or the like has been proposed as the elastic member 4b.
For example, a zinc-plated preserved steel plate processed by pressing, or a metallic foil of stainless steel, phosphor bronze or the like is used as the supporting plate 4a of the elastic blade 4. A charge provision layer made of silicone rubber, urethane rubber or the like subjected to charge control is laminated on the entirety or a part of the surface of the supporting plate 4a by bonding, multicolor forming or the like.
In order to provide a high-quality image or a full-color image by applying an electrophotographic process, for example, the particle size of the toner must be reduced, and more uniform pressure contact with the toner bearing member is required. However, in the conventional elastic blade, there is nonuniform pressure contact in the longitudinal direction of the toner bearing member, resulting in nonuniform charge and, hence, toner having a nonuniform thickness being applied thereto. As a result, a nonuniform image or an image imperfection, such as stripes in an image, or the like, tends to occur.
In order to provide a very precise elastic blade capable of providing uniform pressure contact, there has been an attempt to prepare a supporting plate comprising a steel plate 1.2-1.6 mm thick having a sufficient strength so as not to be deformed when it is mounted in a developing device, and bonding a rubber sheet so that it protudes from a part of the supporting plate. Also, an attempt has been made to form an integrally molded blade by performing injection molding of rubber and inserting the supporting plate. Zinc is plated on the surface of the supporting plate in order to prevent the plate from rusting. A more precise elastic blade can be obtained by performing integral molding than by bonding a rubber sheet. However, when an integrally molded blade is manufactured by performing injection molding of rubber and inserting the supporting plate, the supporting plate is, in some cases, deformed due to the pressure during injection. In order to prevent such a problem, a method of performing injection molding by inserting the plate between molds has been attempted. In this case, however, there is the problem that, when the supporting plate is inserted between molds, the zinc-plated layer of the plate is peeled from the iron surface of the base material due to the surface pressure of the molds and adheres to the molds. If the molding of blades is continued using these molds, the amount of plated layers adhering to the molds increases, thereby causing rubber burr during molding and a change in the size of the molded product. Accordingly, it is necessary to clean the molds.
Furthermore, it has become clear that, since plated zinc on the supporting plate of the molded elatic blade is, thus exposing iron of the base material directly to atmospheric air, rust is generated after assembling the elastic blade in an image forming apparatus. When rust has been generated, the rust leaves the mounted position in the developing device, and is magnetically attracted and fixed on the toner bearing member having a magnet roller incorporated therein which is present near the elastic blade. Particularly, when the rust is attracted on an image developing region, an imperfect image, such as uneven development, stripes or the like, will occur in a developed image on the photosensitive member during development. Even if the toner bearing member does not use a magnet roller, a failure in an image will occur due to adherence of the rust to the developing portion.